DESCRIPTION: (from applicant's abstract): How embryonic cell populations generate specialized cell types at appropriate times, in precise locations and in correct numbers are central issues in developmental biology. The goal of the applicant's laboratory is to understand the mechanisms underlying these processes during neural crest development. To do so, complimentary approaches utilizing the unique experimental advantages of zebrafish and avian embryos will be applied to the question of when and how neural crest cell fates are specified during development, and how the development of specified cells is regulated. The main objectives of this application are to identify fate-restricted cell subpopulations present during the initial stages of neural crest development and to elucidate mechanisms that differentially regulate their development. Two distinct experimental approaches will be employed. First, using clonal analysis techniques and molecular tags for non-overlapping subsets of cells present in initial neural crest populations in avian cell cultures, it will be determined whether the expression of specific molecules are diagnostic of subsequent cell fate. Since the putative diagnostic molecules are growth factor receptors and the activity of their growth factor ligands can be selectively controlled in vitro, the role of these growth factors in the development of receptor expressing cells will be determined. The second approach utilizes mutations in zebrafish that are known to specifically affect the development of neurogenic neural crest cells. Thus, in contrast to the first approach, the molecular identities of the genes disrupted by the mutations are not presently known, but based on the phenotypes of mutant embryos, it is known that both genes are required for neurogenesis during neural crest development. By comparing neural crest development in mutant and wild type embryos, the normal roles of the genes defined by the mutations during neural crest development will be elucidated, and the first step in identifying the genes will be completed.